When commenting on a Working Copy and then checking-in, those comments are copied across to the source node and the topic is suffixed with the previous version number.
e.g. You have content at v1.2, check it out, add comments, check-in to create v1.3
The topics owned by the content are now:
The Share commenting service only displays comments from the "Comments" topic. It should also look for topics suffixed with version numbers and display appropriately.